Drain valves are often provided on aircraft fuel tanks so that liquid within the tank, such as water formed from condensated moisture, may be readily removed or drained. Such drain valves typically include a drain port or opening through which the liquid in the tank is drained and a valve member or poppet that moves in relation to the port to open and close the port. In operation, a preferred form of drain valve has a poppet which is biased to close the port and can be simply pushed inwardly of the fuel tank by use of a screwdriver or other simple tool to open the port. Upon release, the poppet automatically returns to its part-closing position under spring tension. Examples of such drain valves are shown in commonly owned Koller, U.S. Pat. No. 3,703,189 and Koller, U.S. Pat. No. 4,351,355. Another and improved construction is disclosed in, commonly owned Koller, U.S. Pat. No. 4,880,029, the disclosure of which is hereby incorporated by reference herein. These valves have proved reliable and have been commercially successful for a number of years.
A known method of mounting a drain valve to the frame of an aircraft includes the following steps in the order recited. First, the frame or skin of the aircraft is primed with a conventional paint primer. Second, the valve is installed. Third, the valve is masked with a conventional tape, or the like. Finally, the frame of the aircraft is painted.
Part of the design of drain valves used in aircraft is to withstand a wide variety of environmental conditions while maintaining the desired, normally closed position of the poppet. For example, valve components formed of dielectric or non-conductive materials are widely used to improve the capabilities of withstanding and/or avoiding lightning strikes. Likewise, the known devices employ special locking devices and complex constructions to address lightning strike issues. Drain valves are subject to involuntary opening as a result of a lightning strike. During a lightning strike the electric charge from the lightning seeks the least resistant path in order to dissipate the charge. It is believed that the electric charge or arc finds the metal that surrounds the drain valve opening in the aircraft even though careful attention is provided to ensure that the surface is primed and painted, and that no bare metal is exposed. It is also believed that the electric charge or arc results in a very large force concentrated in a relatively small area, i.e., the cracks in the paint. This arc results in a concussion, of sorts, that can crack or even destroy the flange that surrounds the stem of the drain valve. Furthermore, the arc can bypass the valve completely en route to the drain opening.
Accordingly, it is desirable to provide a drain valve and method of mounting the drain valve that encourages diffusion of electric arc into the frame or skin of the aircraft away from the drain opening, and prevents the potential for the energy from a lightning strike from reaching the drain valve opening, thus avoiding the resultant concussion.